1. The Field of the Invention
The present invention is related to illuminant compositions which emit significant quantities of infrared radiation. More particularly, the present invention is related to castable infrared illuminant compositions which exhibit high initial burn rates, burn cleanly, and emit relatively small quantities of visible light in proportion to the infrared radiation emitted.
2. Technical Background
There is a need in various situations for an ability to see clearly at night, or during periods of substantially reduced sunlight. Such situations may, for example, include search and rescue operations, police surveillance, and military operations. In these types of situations, it is often important that key personnel have the ability to see clearly, even though there is limited sunlight.
In order to solve the problem of visibility at night, or during periods of substantially reduced sunlight, devices have been developed which allow one to see based upon available infrared illumination, rather than visible light. While the infrared vision devices take on various configurations, perhaps the most common type of infrared vision devices are night vision goggles. These devices provide individual users with the ability to see much more clearly at night, while not significantly limiting the mobility of the individual user.
In order to facilitate the use of infrared vision devices, it has been found advantageous to enhance the available infrared radiation in the area of interest. In that regard, infrared emitting flare mechanisms have been developed. Such mechanisms have taken on a variety of configurations; however, the most widely used mechanisms comprise flares which emit relatively large quantities of infrared radiation in addition to any visible light that may be produced.
Infrared emitting flares are generally configured in much the same manner as visible light emitting flares. Such flares may provide infrared radiation at a single position on the ground, or they may provide such radiation above the ground. In the case of above-ground operation, the flare system includes an internal or external means of propulsion which allows the user to fire the flare in a desired direction. In addition, the flare itself includes a material which, when burned, produces significant quantities of infrared radiation. In general operation the flare is propelled over the area of interest and ignited. The emitted infrared radiation then greatly enhances the usefulness of infrared viewing devices, such as night vision goggles.
A number of problems have been encountered in the development of suitable infrared emitting compositions for use in such flares. For example, it will be appreciated that it is often desirable to provide an infrared emitting flare which does not emit excessive quantities of visible light. In situations where it is desirable to conduct operations under cover of night with a degree of secrecy, this capability is imperative. Excessive emission of visible light from the flare may alert individuals in the area to the existence of the flare, which may in turn significantly reduce the effectiveness of the overall operation.
It has been found with known infrared flare compositions that excessive visible light is in fact emitted. In that regard, the performance of infrared emitting devices can be judged by the ratio of the amount of infrared radiation emitted to the amount of visible light emitted. This ratio is found to be low for many conventional infrared emitting compositions, indicating a high proportion of visible light being emitted from the flare.
Another problem encountered in the use of infrared emitting compositions relates to the burn rate achieved. Many known compositions have burn rates which are lower than would desired, resulting in less infrared radiation than would be desired. In order to provide an effective flare, relatively high burn rates are required.
It is often observed that the burning (surface area) of the flare composition increases dramatically over time. This characteristic is also generally undesirable. In the case of an infrared emitting flare which is launched into the air, this means that less infrared radiation is emitted when the flare is high above the surface, while more infrared radiation is emitted while the flare is near the surface. Indeed, it is often Sound that the flare continues to burn after it has impacted with the ground.
It will be appreciated that this burn rate curve is just the opposite of that which would be generally desirable. It is desirable to have a high intensity infrared output when the flare is at its maximum altitude in order to provide good illumination of the ground. It is less critical to have high infrared output as the flare approaches the ground simply because the distance between the ground and the flare is not as great (illumination can be expressed by the equation Illumination=(I.times.4.pi.)/(4.pi.R.sup.2) where I is the intensity in watts/steradian, R is the distance in feet from the flare to the object being illuminated, and illumination is expressed in units of watts/feet.sup.2). Ultimately, it is desirable that the flare cease operation before impact with the surface in order to reduce detection and obvious problems, such as fire, which may be caused when a burning flare impacts with the ground.
Another problem often encountered with known infrared emitting materials is "chunking out." This phenomenon relates to breakup or unbonding separation of the flare propellant grain during operation. In these situations it is found that large pieces of the infrared emitting composition may break away from the flare and fall to the ground. This is problematic because the flare fails to operate as designed when large pieces of the infrared producing composition are missing, the amount of infrared output over the subject location is curtailed, and falling pieces of burning flare material create a safety hazard.
It has also been found that the use of conventional flare compositions results in soot formation. Soot formation can adversely affect the operation of the flare device in several ways, including causing an increase in visible light emitted. When soot or carbon is heated it may radiate as a blackbody radiator. Soot formation is encountered primarily due to the fuels and binders employed in the infrared producing composition. Conventional infrared producing compositions have generally been unable to adequately deal with the problem of soot formation.
A further problem relates to aging of the IR emitting composition. It is often observed that known compositions substantially degrade over time. This is particularly true if the storage temperature is elevated. In some situations, it may be necessary to store these materials for long periods of time at temperatures at or above 120.degree. F. This has not been readily achievable with known compositions.
In summary, known infrared emitting compositions have been found to be less than ideal. Limitations with existing materials have curtailed their effectiveness. Some of the problem areas encountered have included low overall burn rates, undesirable burn rate curves, chunking out, poor aging, and undesirable levels of visible emissions.
It would, therefore, be a significant advancement in the art to provide infrared emitting compositions which overcame some of the serious limitations encountered with known compositions. It would be an advancement in the art to provide compositions which provided high levels of infrared emissions, while limiting the level of visible light output. It would be another significant advancement in the art to provide such compositions which had acceptably high burn rates.
It would also be an advancement in the art to provide infrared emitting compositions which substantially eliminated soot formation and which also substantially eliminated chunking. It would also be an advancement in the art to provide compositions which did not readily degrade with age, even when stored at relatively elevated temperatures.
Such compositions and methods are disclosed and claimed herein.